1. Technical Field
The disclosure generally relates to injection molds, and particularly to a multi-cavity injection mold with an improved runner system.
2. Description of Related Art
In recent years, injection mold are widely used for manufacturing workpieces of various fields, such as cars, electric equipments, optical lenses, etc. Conventionally, an injection mold includes a plurality of cavities, and a runner system for injecting plastic into the cavities.
FIG. 4 is a schematic view of a runner system 14 of a conventional injection mold with four cavities 161, 162, 164, 165. The runner system 14 includes a main-runner 141 and three sub-runners 143, 145. The main-runner 141 and the sub-runners 143, 145 are coplanar, being horizontal. The sub-runners 143, 145 include a transverse runner 143 and a pair of longitudinal runners 145. The two longitudinal runners 145 are respectively connected to ends of the transverse runner 143. The main-runner 141 is connected to a middle of the transverse runner 143. The cavities 161, 162, 164, 165 are respectively connected to ends of the two longitudinal runners 145.
During molding, melted material 20, such as plastic, is injected into the main-runner 141, and then flows along the sub-runners 143, 145 to the cavities 161, 162, 164, 165 to form a plurality of workpieces simultaneously. However, when the melted material 20 flows to the sub-runners 143, 145, a temperature of a portion of the melted material 20 at a side of the sub-runners 143, 145 adjacent to the main-runner 141 is higher since the main-runner 141 is located close to a heat source and accordingly has a higher temperature. As it is well known that the viscosity of a fluid decreases as the temperature increases, a speed of the melted material 20 flowing in the sub-runners 143, 145 at the side adjacent to the main-runner 141 should be higher than the melted material 20 at a side away from the main-runner 141. Therefore, after a period of time, the amount of the material 20 flowing into the cavities 161, 162 is more than that into the cavities 164, 165. As a result, the workpieces formed by such an injection mold can not have a homogenous quality.
For the foregoing reasons, therefore, there is a need in the art for an injection mold with an improved runner system which overcomes the limitations described.